The present invention relates generally to the method of bonding together two surfaces of three-dimensional articles of foamed thermoplastic material such as, for example, foamed or expandable polystyrene, foamed polyolefins such as polyethylene and polypropylene and the like. The articles are three-dimensional, as indicated, with substantial length, width and depth dimensions. The bonding together of surfaces of three-dimensional articles becomes a frequent necessity in a variety of industrial applications, with one such necessity being commonly employed in the preparation of molds for fluid metals or malleable substances.
In the preparation of molds for manufacture of metal castings, it has become common practice to utilize a preform prepared from foamed thermoplastic material, specifically expanded polystyrene. These polystyrene masters are normally formed by adhesively bonding segments together so as to form a completed master article for the mold, with such articles frequently having inner cavities or the like to provide complex three-dimensional configurations. In order to prepare the complex configurations of the master, therefore, the master is formed from a plurality of segments, each of which may be, in turn, bonded to one or more others until the entire complex three-dimensional form is completed.
The adhesive bonding of these surfaces becomes reasonably complicated, particularly when foamed thermoplastic materials are being secured together. The adhesive bonding operation is time consuming, and in certain instances, presents dimensional instability problems due to the requirement that the adhesive be retained in a predetermined quantity so as to achieve dimensional stability, within manufacturing tolerances, for the individual thermoplastic masters. In order to achieve the dimensional stability required, it has been found necessary to utilize holding fixtures or jigs which retain the individual components or portions in a desired location for a period of time sufficient to achieve cohesive strength within the bonding material utilized. For most industrial purposes, however, time tolerances are necessary in order to provide appropriate potlife and cure times for the adhesive material being utilized, and when complex forms are utilized, such as foamed thermoplastic materials, heat transfer becomes a problem and hence time-temperature cure functions demand extensive periods of cure to achieve a cohesive mass in the adhesive material.